Jun 19, 2010 10:07 AM

Can someone please help me to identify this caterpillar? I've approached numerous experts and nobody has a clue. It was about 3 inches long on calcareous grassland in Purbeck, Dorset, UK. Spotted in the first week of June this year.

Well, I've circulated it round some of my friends (yes I do have them) and the best guess so far is that it's one of the prominents, some of which have the folded appearance at the bottom of the segments. Colour is wrong though.

As to the size, if the average ant is about 5mm, then the caterpillar is about 50mm or 2 inches. That sounds more reasonable. My wife keeps saying that men can't estimate length anyway......

I too feel it is most like a prominent moth (Notodontidae) but I am not happy with it being any of the UK species unless it is extraordinarily aberrant or these are pre-pupatory colours. A pre-pupatory White prominent?

I will pass this on to the moth folk here at NHM and see if they can reach a conclusion - we love a puzzle!

Chinery says that the Swallow Prominent larva also has a brown form that has pink intersegmental membranes. There are pink areas on this larva but not in the right place. Prominents also tend to have an anal spur which I don't see - although it may be turned away from the photo.

I have to say it looks nothing like any of the White Prominent images on ukleps. It could ineed be closer to 2 inches - everything looks huge through a macro lens! The colouring is perhaps exaggerated by the low sun (see video from opposite side) but this lens renders colour very reliably and I haven't post-processed it in any way .

Ian at ukmoths very kindly got back to me yesterday with a suggestion from Roy this time at ukleps that it might be Black Rustic final instar in an unusual yellow or sick form. He says "Build very similar. Also note the dark marks either side of the spiracles on the first two or three abdominal segments - these match too".

I am not sure what it is but I have heard it is very rare.

Hi mia. I think we settled on Black Rustic unless you have some other info. Not that rare I don't think but unusual to be found in this colouring out in the open at this stage in its development perhaps.